There is disclosed a method and apparatus for laying small-diameter gas, water pipes or the like precisely in the ground. Small-diameter pilot pipes are first laid in while at the same time, a pilot head is measured and controlled to make its straight advance. Pipes of a larger diameter are then laid...http://www.google.ca/patents/US4024721?utm_source=gb-gplus-sharePatent US4024721 - Method and apparatus for laying pipes in the ground
